Historic traffic data for a roadway may include travel time, delay time, speed, and/or congestion data for various times of the day, days of the week, days of the year, and so on. The historic traffic data may be obtained from roadway sensors, probes, and/or incident reporting systems. The sensors may use radar, acoustics, video, and embedded loops in the roadway to collect data that can be used to characterize traffic conditions. For example, sensor data may include speed, volume (number of vehicles passing the sensor per period of time), and density (percentage of the roadway that is occupied by vehicles). The sensor data may include other data types as well, such as vehicle classification (e.g., car, truck, motorcycle).
Probe data is point data collected from a moving vehicle having a device that can identify vehicle position as a vehicle travels along a road network. For example, the device may use cellular technology (e.g., cell handover) or Global Positioning Satellite (GPS) technology to monitor the vehicle's position on the road network. By monitoring the vehicle's movement, the probe data can be used to determine travel time, which can then be used to calculate speed of the vehicle.
Incident data is traffic data regarding a traffic event that obstructs the flow of traffic on the road system or is otherwise noteworthy in reference to traffic. Example incidents include accidents, congestion, construction, disabled vehicles, and vehicle fires. A traffic operator may enter the incident data into a Traffic Incident Management System (TIMS), such as the TIMS described in U.S. Patent Publication No. 2004/0143385, which is assigned to the same assignee as the current application. The traffic operator is a person who gathers traffic information from a variety of sources, such as by monitoring emergency scanner frequencies; by viewing images from cameras located adjacent to a roadway; by calling government departments of transportation, police, and emergency services; and by obtaining information from aircraft flying over the road network.
The historic traffic data may be stored in a historic traffic database, such as NAVTEQ Traffic Patterns™ database, which includes typical traffic speeds for many primary and secondary roads. Data in the historic traffic database may be used in routing applications allowing drivers to plan routes that avoid typically congested areas and receive more accurate trip time estimates based on likely traffic conditions. The historic traffic data may also be used to predict clearance time for a traffic event; to predict traffic conditions when sensor data, probe data, and/or incident data is unavailable for a particular roadway; to predict the probability of accidents; or for any other suitable purpose.
While the historic traffic database has many beneficial uses, there are still opportunities for improvement. One area for improvement is in reducing the storage requirements for the historic traffic database. Because the volume of historic traffic data is so large, it would be beneficial to represent historic traffic data in a manner that minimizes storage requirements.